What are you shooting for with YOUR AFR's ?
05-10-2010, 04:33 PM
#1
What are you shooting for with YOUR AFR's ? What AFR's are you guys looking for on pump gas at WOT ? around 12:1 ?
What about cruise at part throttle? Would 14.6 be a safe number to be at to help the gas mileage? Or is that too lean?
Dare I ask what AFR #'s you guys are seeing (or at least looking for) on spray as well ?
What about cruise at part throttle? Would 14.6 be a safe number to be at to help the gas mileage? Or is that too lean?
Dare I ask what AFR #'s you guys are seeing (or at least looking for) on spray as well ?
05-10-2010, 08:20 PM
#3
At WOT, it depends on the setup. For a N/A motor with a stock intake around 12.8
14.6 at cruise is fine. You can go a little leaner (15.2 or so) if you are looking exclusively for gas mileage.
On spray it depends on the setup. A direct port around a 12:1. A plate fogging or dry system you have to set it up a little richer depending on the size of the shot and the intake style. The stock style intakes have a high pressure area at the back of the intake that causes more air and hence more nitrous to feed into the #7 and #8 cylinders. So these cylinders will be a little leaner and getting slightly bigger shot then the rest. The bigger the shot entering the front of the intake the bigger the bias and the richer you should go. So, a 75 shot I go with the higher 11's, but a 200 plate/dry shot I feel more comfortable in the lower 11's keeping the thing together. Other style intakes (Wieland) make it less of an issue.
14.6 at cruise is fine. You can go a little leaner (15.2 or so) if you are looking exclusively for gas mileage.
On spray it depends on the setup. A direct port around a 12:1. A plate fogging or dry system you have to set it up a little richer depending on the size of the shot and the intake style. The stock style intakes have a high pressure area at the back of the intake that causes more air and hence more nitrous to feed into the #7 and #8 cylinders. So these cylinders will be a little leaner and getting slightly bigger shot then the rest. The bigger the shot entering the front of the intake the bigger the bias and the richer you should go. So, a 75 shot I go with the higher 11's, but a 200 plate/dry shot I feel more comfortable in the lower 11's keeping the thing together. Other style intakes (Wieland) make it less of an issue.
05-11-2010, 02:21 AM
#7
na start 12.6 then adjust from there based on where the car makes power and what the plug says
s/c start around 12.3
turbo start around 11.8
nitrous depends on the size of the hit
Start safe and read your plugs, they are the only thing telling the truth
s/c start around 12.3
turbo start around 11.8
nitrous depends on the size of the hit
Start safe and read your plugs, they are the only thing telling the truth
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05-11-2010, 05:45 AM
#8
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I have found the car will accelerate better if a little rich in the torque band - so I usually go for around 12.5 - 12.6 at peak torque and 12.7 to 12.8 at peak horsepower for NA engines.
A full point lower for FI. And if meth is involved, even richer still (since alcohol stoich is lower to start with).
Nitrous 12.0 to 12.5 depending on the setup.
And for all of them - depend on dyno number changes, track number changes, and plug readings to fine tune fuel and spark.
A full point lower for FI. And if meth is involved, even richer still (since alcohol stoich is lower to start with).
Nitrous 12.0 to 12.5 depending on the setup.
And for all of them - depend on dyno number changes, track number changes, and plug readings to fine tune fuel and spark.
05-11-2010, 09:28 AM
#9
I run 17.0:1 for normal driving (no CATS). If you have CATS, this will kill 'em. Long catalytic converter life requires the A/F ratio to dither just above to just below stoich (14.63:1). 12.7-13.0 WOT, 11:1 CR & 25-26* timing @ WOT on after market high flowing heads. Could probably get 26-27* of timing @ WOT on stock 241 heads. There is no knock; 92 Octane minimum.
